Ion propagation in the magnetosheath

Abstract

The transport of test ions through the magnetosheath depends upon the macroscopic structure defined by the average magnetic and flow fields, B0 and U, and the fluctuating fields, δE and δB, encountered by the particles. In this paper an approximate model is used to generate the macroscopic configuration: it satisfies the jump conditions at the bow shock, treats the magnetopause as a tangential discontinuity (B0 and U tangent to the magnetospheric boundary), and uses intermediate field amplitudes and orientations that resemble the more precise results of gas dynamic simulations. Equations of motion for a fictitious ensemble average particle describe the ion propagation, with the effects of the inhomogeneous turbulence phenomenologically incorporated into a friction tensor whose components reflect the coupling of the ions to the bulk plasma along and across the magnetic field B0. Application to the solar wind releases of lithium ions by the Active Magnetospheric Particle Tracer Explorers mission illustrates the approach: we follow the guiding center trajectory of the ensemble average “particle” for several upstream solar wind and interplanetary magnetic field conditions, different locations of the release site, and quiet and disturbed magnetosheath turbulence regimes. Implications of the results for the release strategy are discussed.